A. Field of the Invention
The present invention relates generally to digital signal transmission, and more particularly, to a system and method for transmitting control information together with a multiplex of digital services, including imaging services, for selective display of the services at a plurality of remote locations.
B. Description of the Relevant Art
With the growing trend toward a merger of the previously separate technologies of telecommunications including voice and data telecommunications and television including satellite, broadcast and cable television, there has emerged an increased interest in developing adaptable transmission systems capable of handling any one or more of a collection or plurality of such services. The primary media investigated for providing such services to date comprise, for example, coaxial cable, land-based microwave, so-called cellular radio, broadcast FM, broadcast satellite and optical fiber, to name a few.
Each media has its own characteristics. For example, comparing cable and satellite for digital data transmission, cable tends to have a medium error rate, but, when errors appear, the errors come in long bursts. Satellite as a media has a pretty poor error rate, primarily due to the requisite weak signal power, and hence, low signal to noise ratio. In satellite, then, the poor error rate is specially corrected utilizing such techniques as convolutional error correctors, not required in a cable environment.
In copending U.S. application Ser. No. 07/968,846 filed Oct. 30, 1992 and entitled "System and Method for Transmitting a Plurality of Digital Services," now U.S. Pat. No. 5,400,401, there is described an encoder for generating a multiplexed data stream carrying services to remote locations via, for example, a satellite or a cable distribution network. The generated data stream comprises a continuous sequence of frames, each frame comprising two fields, and each field comprising a plurality of lines. A first group of lines of a field defines a transport layer and a second group of lines defines a service data region. A feature of the disclosed scheme is the ability to dynamically vary the multiplexed data stream from field to field. A further feature of the disclosed scheme is that the data transmission rate of the multiplexed data stream is related to the frequency of known analog video formats, i.e. frame, field and horizontal line rates.
In U.S. application Ser. No. 07/970,918 filed Nov. 2, 1992, entitled "System and Method for Multiplexing a Plurality of Digital Program Services for Transmission to Remote Locations," now U.S. Pat. No. 5,319,709, there is described another system, this for multiplexing a plurality of digital program services comprising a collection of, for example, video, audio, teletext, closed-captioning and "other data" services. According to the disclosed scheme, a plurality of subframe data streams are generated, each having a transport layer region and a program data region. These subframe data streams are then multiplexed together into superframes having a transport layer region and a subframe data region.
While these disclosed transmission systems permit a variety of services to be transmitted over various media to remote locations, there remains a need to provide yet other alternative arrangements more particularly adapted to the wide variety of services that may be offered over various media and permit the end user at the remote location greater flexibility over the data content the user is ultimately enabled to receive. Moreover, such a system should be able to be easily adapted to transmit an increasing number of different services in an increasingly efficient manner, for example, utilizing the same or less bandwidth.
When such a variety of services are transmitted, it is desirable for system operators to exert various forms of authorization control over the services transmitted to a user. By using authorization control, the system operator can make a set of services available to some users but not to others. The forms of authorization control desired by the system operators may differ depending on a classification of the service provided, a classification of the user receiving the service, or both.
Such authorization control includes implementation of a blackout, whereby one or more services are denied to a user according to a predetermined classification. For example, broadcasters may be prohibited by contract from broadcasting a sporting event to users within a fixed distance from the stadium, arena, or track where the sporting event takes place in order to protect ticket revenues. In current systems, the decoder at the user's location calculates whether a blackout is required according to a complicated, three-dimensional mathematical algorithm. Of course, the decoder must be equipped with a processor capable of performing the calculations. If such a processor is already provided in the decoder, the processor must be diverted from other jobs to perform the complex calculations necessary to determine whether the decoder is within the blackout area. Accordingly, the speed of processing is reduced.
Users may also be classified for blackout purposes by region, for example, by city or county. This regional blackout authorization control is currently available in certain B-MAC (B-type Multiplexed Analog Component) products. Spotlighting is another type of authorization control where one or more services are provided only to a predetermined class of users. Thus, spotlighting may be considered as the inverse of blackout.
The group authorization is implemented as follows. Each decoder is sent an addressed data packet which specifies the group to which the decoder belongs. System data includes seeds and control information, and two bytes are used to send CSACS packets. CSACS packets send the entire authorization stream in a list of group codes. If a decoder is a member of a listed group, it uses the CSACS package authorization description. If the decoder is not a member of the listed groups, it is not authorized. Accordingly, a blackout can be implemented by removing a group to be blacked out from the transmitted list.
Over several sessions, control such as audio routing and mute controls, data mute control, video on/off, etc. is transmitted via the CSACS method of group authorization so as to extend the available bits of system data. However, this information would be sent in one session if allowed by the system data. In addition, as indicated above, reception of a CSACS cycle was required to make authorization possible.
Authorization control may also be used by the broadcaster to offer a variety of service packages to users at different prices. This is called tiering, and the various service packages available to users are called tiers. In B-MAC applications, a single tier pointer is transmitted. The tier pointer references a bit string in the decoder. If the bit pointed to by the tier pointer is in a first state, authorization occurs. If the bit pointed to is in a second state, authorization is denied.
The operator is afforded maximum flexibility if the system can support numerous authorization control schemes. However, as more authorization control schemes are provided, an increasing portion of the transmitted signal must be dedicated to authorization control information. As a result, less capacity is available for the transmission of services. In addition, a significant amount of time may be needed for a decoder to decrypt authorization control information encrypted by the broadcaster at an encoder. Furthermore, the need for certain authorization schemes may vary over time as conditions change. Therefore, an operator may waste a significant portion of transmission bandwidth by providing for authorization control schemes that are not in use.